1. Field of the Invention
The present invention relates to ionic bond containing polymers and more particularly to polymers modified so as to be capable of being formed into a film by the Langmuir-Blodgett method.
2. Description of Prior Art
It was found by Langmuir and Blodgett in 1930s that fatty acids having ca. 16 to 22 carbon atoms can form a monomolecular film on the surface of water and such films can be built-up or laminated on a substrate. However, it is only in recent years that investigations on their technical application has been started.
Investigations which have heretofore been made are summarized in Kotai Butsuri (Physics of Solids), 17 (12), p. 45 (1982); Thin Solid Film, 68, No. 1 (1980); ibid., 99, Nos. 1, 2 and 3 (1983); G.L. Gains, Insoluble Monolayers at Liquid-Gas Interface, Interscience Publishers, New York (1966); and so forth. However, conventional Langmuir-Blodgett films (hereinafter referred to as "LB films") of saturated straight chain carboxylic acids are not satisfactory in heat resistance and mechanical strength and, therefore, cannot be put into practical use as they are.
In order to rectify the above disadvantages, investigations have been made on polymeric films of unsaturated fatty acids such as .omega.-tricosenic acid, .omega.-heptadecenic acid and .alpha.-octadecylacrylic acid, fatty acid unsaturated esters such as vinyl stearate and octadecyl acrylate, or diacetylene derivatives, for example. These films, however, are not sufficiently high in heat resistance and cannot be said to be excellent in electrical properties.
It is known that hydrophilic group-containing polymers such as polyacrylic acid, polyvinyl alcohol, polyethyl acrylate and polypeptide also have film-forming properties. No investigation, however, has been made on modified polymers to be used as a material, particularly for preparation of LB films, and an excellent LB film material has not yet been discovered.
Polyimide provides a heat resistant film. The thickness of polyimide film produced by techniques such as spin coating is greater than 1,000 .ANG.; usually, a heat resistant thin film having a thickness of from 1 .mu.m to 1,000 .ANG.and with no pinhole formed therein is very difficult to produce.
On the other hand, a polyimide film is known as a heat resisting film but in the case of forming the film thereof by spin coating, etc., which is known to be a coating method for forming the thinnest film of such a polymer, the thickness of the film formed is at best not thinner than 1,000 .ANG.and is usually thicker than about 1 .mu.m. In other words, it is very difficult to form a heat resisting thin film of thinner than 1,000 .ANG.having no pinholes by using such a polymer.